Idler Spindle stripped threads

[tomkilde]

The threads on the end of my idler spindle (67-0707) are badly stripped, almost smooth, so the dynamo drive sprocket (67-0721) cannot be securely fastened.  I looks like a previous owner used the wrong type of nut.  Does anyone know of a work-around solution for attaching the sprocket?  Or is replacing the spindle my only option?

1961 A10 Super Rocket

[RDfella]

Remember a coarser thread is a deeper thread - one reason why cycles used the bscy fine pitch, so they could thread thin tube. So, for example, if your thread is 5/16 bscy, a 5/16 bsf or preferably whit thread (whilst being a bodge) would likely give you enough grip to hold that taper. If it's 1/4" then M6 comes to the rescue - bit smaller dia and coarser thread as well.

[muskrat]

G'day Tom.
The original thread is 3/8 cei so as RD says a 3/8 whit or unc may give you enough clamping force for the taper.
Cheers

[RichardL]

The threads on the end of my idler spindle (67-0707) are badly stripped, almost smooth, so the dynamo drive sprocket (67-0721) cannot be securely fastened.  I looks like a previous owner used the wrong type of nut.  Does anyone know of a work-around solution for attaching the sprocket?  Or is replacing the spindle my only option?

1961 A10 Super Rocket

At Baxter Cycle. You're not actually in Nebraska, so that puts the kabosh on driving over and picking it up, but you could have it fairly soon and still afford dinner.

 https://www.baxtercycle.com/product/67-0707/

Richard L

[trevinoz]

You could try machining the thread of and drilling and tapping the shaft for a stud or bolt.

[RichardL]

You could try machining the thread of and drilling and tapping the shaft for a stud or bolt.

Trev,

That sounds like it could be more work, especially since he could easily buy a new (to him) spindle. Also, we don't know that he has a lathe. I think Baxter can probably sell him a new nut, as well.

Richard L.

[groily]

I guess it comes down to whether a bodge could pass muster. Yes, tapers do the work - but the darn nut has to stay on  . . . I'd be uneasy just running another die up the thing, have to say, unless - maybe - I could cross-drill the shaft and use a castellated nut and a small split pin to be certain it couldn't fall off. Or something.

I'm the first to do things that aren't 'correct spec' when faced with these sorts of things, but I'm a bit picky about the execution of workarounds.
A bodged fastener whirring round in there would worry me (needlessly possibly, but it would), so I would either do what Trevinoz suggests, which would be a workmanlike solution, or I'd turn off the rest of the dud thread and put on a new one (of whatever series required the least reduction in diameter to get to the exact size for the die).

I would then make a new nut from a bit of hex the same AF or near as dammit as the original, tapping it to be a good 90% fit (ie a bit more than typical), and thereby ensure that the thing sat just like the original.

To do either properly it does needs a lathe, I know. But  . . .

Or I'd get another shaft if they can be had.

[tomkilde]

Thanks for the suggestions.  I have the correct tap & die set, but I'm not a machinist, so cutting new threads seems a little daunting.  And I've spent so much time and energy (and money) fixing the previous owners' bodges that I don't want to add a new one.  I've placed an order with Baxter for the new spindle.  I used a lot of different resources when I restored the bike, but Baxter was always my favorite.

BTW this issue came up because I finally decided to tackle the non-functioning charging system.  The dynamo needed a new armature and now works perfectly, at least on the bench.  Once the bike is put back together again I'll check on the regulator, which is original.  Based on what I've read in the forum, a DVR2 seems to be the best option if the regulator needs replacement.

[groily]

I think you are really wise.
Don't risk spoiling things for a ha'pence worth of tar as they say!
And yes to a DVR, as others have said. Most excellent devices, reliable and long-lasting. There are other good ones, but the DVR2 edges them all for me. I've fitted them on all sorts, Lucas, Miller, Bosch, even elderly Hardly-Ablesons from back in the day (with mods to the dynamos) - and they have done really well.

[bikerbob]

While you are solving this problem you might want to consider fitting a toothed belt drive for the dynamo it increases the speed of the dynamo by about 10% and makes a big difference to the charging. Before I fitted one you had to be above 30mph  to maintain a  charge with the headlights on now with the toothed belt it is still showing a charge at 20mph.

[Jules]

Could you provide a link for that conversion please BB??

[a10rgs]

here you are:

https://shop.srmclassicbikes.com/product/dynamo-belt-drive-kit-a7-a10-1950-1963

[groily]

Or
https://dynamoregulators.com/drive-belt-kit.php
which is now supplied by Steve McFarlan of leccy leg fame. Details on his site https://startyourbsa.co.uk/product/ if you scroll down

Both conversions are good. Having used both for serious mileages, I preferred the heavier duty version from the DVR2 guys.
My SRM one developed slipping pulley syndrome at about 15K miles - and damaged tapers are a quite hard fix. I got round it by using the steel centre / taper from the original sprocket, riveted to the middle of the ali SRM pulley.

In either case, it's possible that a little bit of casting may have to eased off to get clearance for the large pulley - depending on exactly how fine the walls are on the inner timing cover. (But no big deal.)

[Greybeard]

https://dynamoregulators.com/voltage-regulators.php
That link can provide a DVR2 and a belt conversion kit.

[bikerbob]

According to the Dynamo regulator website it has been discontinued they have no more stock.